For tiny Devils Hole pupfish, startling video shows it must have felt like a “huge tsunami” when violent water-level oscillations from an earthquake 300 miles away disturbed the small ledge they live on in a single Mojave Desert cavern pool for some 15 minutes.

These water-level oscillations in the cavern in Death Valley National Park were caused by the magnitude 7.2 El Mayor - Cucapah earthquake and an immediate aftershock that occurred on April 4.

The video from four U.S. Geological Survey cameras shows significant water-level oscillations, causing great disturbance to the shallow feeding and spawning shelf critical for the continued existence of these fish, said Ambre Chaudoin, a graduate student in fisheries with the USGS Arizona Cooperative Fish and Wildlife Research Unit at the University of Arizona, Tucson.

“The shelf substrate sediment was largely redistributed as a result of the water oscillations,” said Chaudoin. “Such disturbance can be important because the spawning shelf is less than 13 feet long and 7 feet wide, smaller than many walk-in closets.”

Federal and state surveys done within a week after the April 4 earthquakes revealed about 118 individual fish in the pool, an increase from about 70 the year before. Also, biologists saw newly hatched larval fish and evidence that the fish were spawning.

The violent oscillations, though, washed away algae that are essential to the food web of the critically endangered fish, though biologists hope they will grow back quickly. Biologists with the National Park Service, U.S. Fish and Wildlife Service and the Nevada Department of Wildlife will carefully monitor Devils Hole for any harmful after-effects to the fish.

Ambre and fellow USGS researcher Olin Feuerbacher happened to be conducting Devils Hole pupfish behavior surveys on April 4, the day the earthquake struck. They caught the earthquake-induced wave action on video cameras they had just reconnected to their recording position inside the pool 10 minutes before the quake struck.

“The fish begin to move out of the camera’s view as the waves start getting bigger, and then, because of all the sediment being stirred up, you can’t see the fish. As the waves grew stronger, the fish likely moved into deeper waters,” she said.

Paul Barrett, a FWS biologist who leads the Devils Hole Pupfish Recovery Team, said that water-quantity and -quality changes after an earthquake can affect sensitive aquatic environments by changing water levels or by reducing the amount of algae or invertebrates that live on the ledge. But sometimes they can be beneficial as well.

“Earthquakes, such as a 1978 temblor in Mexico, can set up waves that clear the spawning shelf of the algae upon which the pupfish rely, however depending upon the time of year, the algae may regenerate quite rapidly,” said Barrett. “Furthermore, quakes can serve a useful purpose in shaking silt and other fine particles that have washed into Devils Hole off of the spawning shelf and into the deeper waters. This frees important space between the substrate particles where the Devils Hole pupfish larvae seek refuge.”

In fact, said Barrett, after the April 4 Mexicali quake, the National Park Service recorded a slight increase in larval abundance as compared to a similar survey a few weeks before the earthquake occurred.

The phenomenon of earthquakes and corresponding seismic effects on water wells, streams, springs, seeps and lakes is well known. Generally, large earthquakes (greater than magnitude 6.0) with epicenters hundreds to thousands of miles away can cause hydrologic responses in water wells and surface-water bodies. Hydrological effects from the April 4 earthquake were also noticed in places as far away as Virginia.

Devils Hole pupfish populations remained about 400-500 individuals until the late 1960s when the water level in the pool dropped in response to pumping of nearby irrigation wells. Pupfish numbers declined precipitously, and though water in Devils Hole is now maintained at a minimum level, the pupfish are still greatly imperiled. With intensive management efforts, pupfish numbers are increasing from a critical low of just 38 individuals in 2006 to about 118 in the 2010 spring survey after the recent temblor.

Although Chaudoin and USGS researcher Olin Feuerbacher said they would have liked to have seen first-hand the effects of the quake on the hole, they were fortunate in having removed the tiny viewing platform they had been sitting on right above the pool before the quake hit. “Our viewing platform is about 50 feet below ground level, only a few inches above the water surface of the pool,” said Chaudoin. The earthquake caused water to hit our cameras about 4 feet above the platform, so it probably would have been a rather unpleasant experience if we had been on the platform,” she said.

The USGS scientists are using video to help them assess relationships between environmental conditions and spawning in the pupfish to help managers better understand the habitat and spawning requirements and ultimately help in captive propagation. This study is being conducted by the USGS Arizona Fish and Wildlife Cooperative Research Unit and is funded by the U.S. Fish and Wildlife Service, in partnership with the National Park Service and Nevada Department of Wildlife.

About Devils Hole Pupfish

Contained deep within a limestone cavern in the Mojave Desert, Devils Hole is a constant temperature, 10 by 50 foot pool of water that provides a window into the extensive carbonate aquifer within the Amargosa Valley groundwater basin. Devils Hole pupfish live only in Devils Hole, dependent on a tiny spawning shelf less than 13 feet long and 7 feet wide. There, these colorful fish – the males a sparkling blue, the females a more subdued grey-blue or silvery-blue – have made their home for thousands of years near the upper limit of its temperature tolerance – the water remains around 93 degrees -- and near the lower limit of its oxygen tolerance. Adult fish average only about one inch in length and are unique among pupfish in lacking pelvic fins.

Each spring, just enough sunlight penetrates Devils Hole to allow food in the form of algae and small invertebrates to grow in the spring. This food supports a new generation of pupfish before the previous year’s fish die of old age. No one knows how deep the pool is, but the pupfish live in the upper 80 feet of the pool.